fix: missing-dep [add] button respects MOD_ID_ALIASES on build mismatch

When user is on B42 and a mod requires the B41 mod_id (e.g.
truemusic_mixtape_megapack require=truemusic), the canonical wsid
(2613146550, B41-only) is rightly filtered out by the build guard —
but we were silently dropping the suggestion. Now we fall back to
MOD_ID_ALIASES: truemusic → TrueMoozic, suggest wsid 3632610172.

- _lookup_wsids_for_missing returns Dict[str, Tuple[wsid, suggested_mod_id]]
- build_warnings unpacks tuple, label clarifies rename when alias used
- adapters.build_response signature updated for new shape

api/app.py

@@ -228,20 +228,29 @@ async def _lookup_wsids_for_missing(
     conn,
     mlos_warnings: Dict[str, Any],
     pz_build: Optional[str] = None,
-) -> Dict[str, str]:
+) -> Dict[str, Tuple[str, str]]:
     """Resolve missing-requirement mod_ids to wsids via mod_parsed cache.
 
-    Returns {mod_id -> workshop_id} for any missing dep we've previously
-    cached. Used to render an [add to list] action button next to the
-    'missing' warning. Unknown deps just get no button.
+    Returns {missing_mod_id -> (workshop_id, suggested_mod_id)} for any
+    missing dep we've previously cached. `suggested_mod_id` matches the
+    missing mod_id by default, but when the canonical wsid is wrong-build
+    AND `MOD_ID_ALIASES` (adapters.py) has an alternative whose cached
+    wsid IS build-correct, we redirect to the alias. Example: user on B42
+    has `truemusic_mixtape_megapack` (require=truemusic). truemusic only
+    exists as a B41 wsid; the alias `TrueMoozic` exists as a B42 wsid.
+    Result: {"truemusic": ("3632610172", "TrueMoozic")} — frontend renders
+    [add TrueMoozic] pointing at the correct build's wsid.
 
     pz_build filters out wrong-build resolutions: if the user is on B42 and
-    the only cached wsid for `dep` is tagged `Build 41` only, we DROP the
-    suggestion. Adding it would just trigger a build-mismatch warning;
-    worse, in cases like `TacHold requires modoptions` where the author's
-    `require=` is over-declared, the suggestion misleads the user toward
-    a B41 mod that doesn't actually need to be in the load order.
+    the only cached wsid for `dep` is tagged `Build 41` only, the canonical
+    suggestion is DROPPED (and the alias path may rescue it). Adding the
+    wrong-build dep would just trigger a build-mismatch warning; worse, in
+    cases like `TacHold requires modoptions` where `require=` is over-
+    declared, the suggestion misleads the user toward a B41 mod that
+    doesn't actually need to be in the load order.
     """
+    from adapters import MOD_ID_ALIASES
+
     missing = mlos_warnings.get("missing_requirements") or {}
     if not missing:
         return {}
@@ -252,6 +261,11 @@ async def _lookup_wsids_for_missing(
                 wanted.add(d)
     if not wanted:
         return {}
+    # Expand the fetch set with alias targets so we can resolve in one round.
+    for dep in list(wanted):
+        for alias_target in MOD_ID_ALIASES.get(dep, []):
+            wanted.add(alias_target)
+
     rows = await conn.fetch(
         """
         SELECT DISTINCT ON (mp.mod_id) mp.mod_id, mp.workshop_id, wm.tags
@@ -268,15 +282,36 @@ async def _lookup_wsids_for_missing(
     other_tag = "Build 41" if target_tag == "Build 42" else (
         "Build 42" if target_tag == "Build 41" else None
     )
-    out: Dict[str, str] = {}
+
+    def _is_build_correct(tags: List[str]) -> bool:
+        if not target_tag or not other_tag:
+            return True
+        return not (other_tag in tags and target_tag not in tags)
+
+    # candidates: mod_id -> (wsid, build_correct)
+    candidates: Dict[str, Tuple[str, bool]] = {}
     for r in rows:
-        if target_tag and other_tag:
-            tags = list(r["tags"] or [])
-            if other_tag in tags and target_tag not in tags:
-                # Wrong-build only — adding it would just trigger a
-                # build-mismatch. Skip the suggestion.
-                continue
-        out[r["mod_id"]] = r["workshop_id"]
+        tags = list(r["tags"] or [])
+        candidates[r["mod_id"]] = (r["workshop_id"], _is_build_correct(tags))
+
+    deps_seen: set = set()
+    for deps in missing.values():
+        for d in deps:
+            if d:
+                deps_seen.add(d)
+
+    out: Dict[str, Tuple[str, str]] = {}
+    for dep in deps_seen:
+        cand = candidates.get(dep)
+        if cand and cand[1]:
+            out[dep] = (cand[0], dep)
+            continue
+        # Canonical missing or wrong-build; try aliases in declaration order.
+        for alias_target in MOD_ID_ALIASES.get(dep, []):
+            alt = candidates.get(alias_target)
+            if alt and alt[1]:
+                out[dep] = (alt[0], alias_target)
+                break
     return out